30 ml of a 6N aqueous hydrochloric acid solution are added to a solution of 1.77 g of benzyl [4-(5-methoxy-1-methyl-1,2,3,6-tetrahydropyridin-4-yl)-2-(propan-2-yloxy)phenyl]carbamate in 60 ml of THF. The reaction medium is heated at 50° C. for 2 h 30 and then evaporated to dryness. The residue is taken up in 15 ml of water, 5 ml of a saturated aqueous sodium carbonate solution and 50 ml of ethyl acetate. The two phases are separated, and the aqueous phase is washed with twice 15 ml of ethyl acetate. The combined organic phases are dried over magnesium sulfate, filtered and evaporated, so as to give 1.7 g of benzyl [4-(1-methyl-3-oxopiperidin-4-yl)-2-(propan-2-yloxy)phenyl]carbamate in the form of a brown gum.
